Recently, as miniaturization is increasingly demanded, a relatively high frequency power needs to be supplied to generate high density plasma. As depicted in FIG. 6, as a frequency of a power supplied from a high frequency power supply 150 becomes higher, a high frequency current flows along a surface of a lower electrode 110 and particularly, along a top surface of the lower electrode 110 from an edge area of the lower electrode 110 toward a central area thereof by a skin effect. Accordingly, electric field intensity at the central area of the lower electrode 110 becomes higher than electric field intensity at the edge area of the lower electrode 110, so that ionization or dissociation of a gas is accelerated at the central area of the lower electrode 110 as compared to the edge area thereof. Consequently, electron density of plasma at the central area of the lower electrode 110 becomes higher than electron density of plasma at the edge area thereof. At the central area of the lower electrode 110 where the electron density of plasma is high, resistivity of plasma becomes low, and, thus, the high frequency current is concentrated at a central area of an upper electrode 105 facing the lower electrode 110 and plasma density becomes more non-uniform.
In order to improve uniformity in plasma, it has been suggested to embed a rectangular-shaped flat dielectric member in a lower center of a conductor of an electrode (for example, see Patent Document 1). In Patent Document 1, an intensity distribution of an electric field is decreased under the dielectric member by action of the dielectric member, so that plasma density at the lower center of the electrode becomes decreased and uniformity in the plasma density can be improved.
In order to further improve uniformity in plasma, it has been suggested to form a dielectric member embedded in a conductor of an electrode into a taper shape (for example, see Patent Document 2). In Patent Document 2, since the dielectric member is formed into a taper shape, an intensity distribution of an electric field at an edge area of the dielectric member is not too much decreased as compared to a case in which the dielectric member is flat. Accordingly, uniformity in plasma density can be further improved.    Patent Document 1: Japanese Patent Laid-open Publication No. 2000-323456    Patent Document 2: Japanese Patent Laid-open Publication No. 2005-228973
However, in order to embed the dielectric member in the conductor, a method of connecting different kinds of materials is needed. Particularly, in order to embed the taper-shaped dielectric member in the conductor, a large-scale taper structure needs to be manufactured. By way of example, the conductor and the dielectric member may be connected to each other by an adhesive or a screw. Further, the conductor may be made of metal such as aluminum or the like and the dielectric member may be made of ceramic or the like, and, thus, a linear thermal expansion coefficient is different. Therefore, an appropriate gap may need to be formed at a connecting area between the conductor and the dielectric member. However, if the dielectric member is formed into a taper shape, it is difficult to perform a machining process thereto and a dimensional accuracy at a tapered area becomes deteriorated. Accordingly, a stress may be concentrated on a part of the connecting area due to a difference in a linear thermal expansion coefficient, and, thus, the adhesive on a connecting surface may be peeled off and may become a contaminant within a chamber.
If an attempt to change a profile for an effect of a plasma process is made, since the dielectric member is embedded in the conductor, a broad scale design needs to be changed. Even if the effect of the plasma process is slightly changed by making a partial change of the design, a manufacturing process is still difficult. Therefore, in order to overcome the above-described problems, it is necessary to manufacture an electrode capable of controlling an intensity distribution of an electric field by using a single material or a material to be integrated.
In order to solve the above-described problems, the present disclosure provides a novel and advanced electrode and a plasma processing apparatus capable of controlling an intensity distribution of an electric field of a high frequency power used for generating plasma by using the electrode made of a homogeneous material.